Mortise and tenon questions

[jussi]

1. I used my Shop Fox mortiser for the first time and notice it leaves very uneven bottom. How crucial is it for the bottom of the mortise to be flat? My initial thought was that most of the strength comes from the long grain to long grain connection. Is this correct?

2. With the very jagged bottom left by the mortiser the tenons never bottom out. Is this important? Again my thought here was that as long as the shoulders (hope that's the right term) is flush then that's all that's important.

3. How do you cut your tenons? I've seen them both with a tenoning jig and a dado set? I used the latter because I figured I could cut them larger than desired initially and then slowly creep up to a tight fit. Would it be just as easy (or easier) with a tenoning jig.

4. Should I just ditch the mortiser and strictly use a router to get the flat bottoms?

5. Been thinking about getting a shoulder plane to fine tune the tenons? Worth it or is it just a luxury item? Finances wouldn't allow me to get it any time soon but I thought I do some research for the time being.

[chopnhack]

From my limited experience:
1. It's not important and yes you are correct

2. Either shorten the tenon or deepen the mortise - whichever is more practical - you dont want the tenon to bottom out but you do want the shoulders to touch the other workpiece

3. Router and chisel and just by chisel in the past.

4. Really don't need flat bottoms

[LCHIEN]

i agree with chopnhack.
the end of the tenon does not have to mate and adds no strength - its the contact along the long grain of the shoulders that is glued for strength.

the bottom of the mortise will not see the light of day once mated.

[Tom Hintz]

That "uneven" bottom in the mortise can serve a purpose. When you insert the glued-up tenon glue get pushed ahead of it as it gets scraped/squeezed off of the sides. That little space at the bottom of the mortise gives the excess glue a place to go and helps prevent hydraulicing the joint where the tenon wants to push back out or prevent it from seating fully. Even when i cut mortises with a router, I cut them 1/8" or so deeper than the tenon to make sure there is some room for glue in there.

[drumpriest]

I used to do all of my mortises by router, as shown here

http://www.bt3central.com/showthread.php?t=27419

but I have gotten a domino joiner now, which is still a router, just a special purpose one. I rarely deal with integral tenons, to be honest, always found it easier to use loose tenons and make up the stock in batches.

A flat bottom isn't a requirement, just so long as it's slightly deeper than needed as these guys have mentioned, the excess glue can go there.

[cabinetman]

I also agree there should be a gap. Since dowels can be considered a loose tenon, the gap reasoning holds for them too. A well fitted joint can also present an "air lock", when glue is used. The glue can create the "seal". A tenon (or dowel) can be forced out, or not be able to be seated under those conditions. For dowels, fluting can relieve the "seal" for both glue and air. For an M&T with a tight fit, some light scoring will help.

Over gluing should be prevented and a very light coating on the mating parts is usually sufficient.
.

[SARGE..g-47]

I always cut my mortice about 1/8" deep on purpose for the reasons already mentioned. Glue on end grain provides no real strengh as long grain is the key. As far as tenons.. I have cut them by hand.. band-saw.. router.. and tenoning jig. I purchased one of those univeral tenon jigs on sale and frankly... that's how I do it now as surprisingly the jig can be adjusted to be exact with a little assist from the operator.

You are better off cutting them proud (over-size) than under-size. If you under-size one you have to glue a piece of veneer on to attain over-size so you can take it back to just right. ha.. ha... But.. I work loose in winter when the wood is usually at it's lowest moisture content and tight in summer when it is at it's usual highest with my deep south humidity.

You are fine cutting them with your Shop Fox. I used one for about 7-8 years before I got my current little mortise machine. Every type of hollow mortise chisel machine is going to leave a somewhat ragged bottom as the spur on the bit has to slightly exceed the end of the chisel to take the main waste out. The chisel merely collapses what is left after the bit drills out the main waste.

BTW.. a shoulder plane will work but you really only need to cut the tenon over enough so a few passes with a rasp on each side leaves a glove fit. So.. shoulder planes are useful but you necessarily need one. But.. if you ain't got a rasp and files for this and other task.. get one as they are essential in making many joints.. edge profiles and other fine tune details.

Again.. every mortice machine will leave a ragged bottom by design.. every machines but it doesn't matter as many have stated. Enjoy...

[JimD]

I use a Jet hollow chisel mortiser. I make a second pass on my mortises where I take tiny little bites, going forward only about 1/8 inch or so at a time. It cleans up the bottom some. It still is not smooth, like a routed mortise, but it is better. I also cut them a little extra deep, like 1/8. Before I started nibbling a pass, it was too rough at the bottom to work with the mortise only 1/8 deep.

I usually cut tenons using a homemade jig that rides on the rip fence of my BT3100. I have the micro-adjuster for the rip fence and find it very handy for getting the tenon the right thickness. I like to cut the cheeks with a miter gauge on the bt3100. I have an Osborne I use with home-made accessory tables on the BT3100. I also sometimes just make deep cuts with the jig.

If you want to get the best possible fit of your mortise and tenon joints, I think you will want to save up for a shoulder plane or switch to loose tenons. I've tried a bunch of ways of cutting tenons and I sometimes get them nice and tight but if I have a project with 10 tenons, at least 1 or 2 will need a little trimmed off the shoulder. With a shoulder plane, a pass or two and I have a nice tight fit. Without it, I have found no reasonable way to do this. I've read about people doing this by sanding but it never worked for me.

Jim

[jussi]

Thanks for the advice and the lesson guys. I guess I'll be keeping my mortiser after all.

I have a tenoning jig as well and will give that a try next to see if I get tighter results. I found it a little hard to get micro adjustability on the blade height of the TS when using a dado set. I would get the tenons just proud and then when I made the next pass I would take off too much. My thought was that I was getting some backlash (similar to that of a router lift)? Man I wish wixey made a tablesaw height gauge. Which is why I thought a shoulder plane would work better for that last little cuts.

Sarge, I do have a rasp I got a garage sale a while back but have never really used it. I had never thought of it on tenons. I'll give it a try next time.

Jim, thanks for the advice on using the mortiser. I'll keep that in mind.

One last question on the subject. How snug do you guys think the joint should be. Snug enough so you need to be able to hammer it in or just enough so you could push it in (with some force) by hand.

[cabinetman]

One last question on the subject. How snug do you guys think the joint should be. Snug enough so you need to be able to hammer it in or just enough so you could push it in (with some force) by hand.

Hammered in is way too tight. There should be slight friction dry if its a good fit. With glue will insert without a lot of force. Hard to explain, its more of a feel.
.

[scmhogg]

I have one of those heavy metal tenoning jigs like the one shown. It allows you to micro-adjust. And, best of all it feels really safe.



You can do a lot better than the Delta price shown. I can't remember the manufacturer, but it cost less than $50 at WW show.

BTW, it won't make the bottoms look any better, but it will make it a lot easier to use your mortiser, if you lap the outside of the chisel and use a conical stone to sharpen the inside. I have the cheap HF chisels and they work like a champ with a little care.